GIF

GIF dates to 1987 and is best known today for animated short clips. The format is limited to 256 colors per frame, which is why photographic GIFs look blotchy, but for low-color animations and reaction loops it's the universal compatibility format. For any animation longer than a few seconds, MP4 is dramatically smaller (often 10-20×) and every social platform converts uploaded GIFs to MP4 internally.